Shortly after the closure of neural tube, functionally distinct groups of neurons differentiate in specific locations. For example, motor neurons differentiate in the ventral horn whereas sensory neurons differentiate in the dorsal horn of the spinal cord. The mechanisms by which a relatively simple neural tube achieves its characteristic pattern and polarity are unknown. The results of our preliminary studies suggest that the floor plate, specialized neuroepithelial cells located in the ventral midline of the neural tube, may contribute to the establishment of the basic organization in the neural tube. The objective of this proposal is to test the hypothesis that the floor plate influences cellular differentiation and establishes pattern and polarity in the developing CNS. The specific aims are: (1) Determine the influence of floor plate on the development of the motor neurons in the spinal cord. Ascertain if floor plate is responsible for inducing nearby cells to differentiate as motor neurons. (2) Examine the effect of floor plate on the development of the dorsal horn sensory neurons. Determine whether floor plate inhibits more distal cells from becoming motor neurons or the differentiation of motor neurons secondarily influences development of sensory neurons. I will test the first aim by experimentally inducing an additional floor plate on the dorsal surface of the neural tube in quail embryos and then evaluate whether motor neurons differentiate in the dorsal horn. Whether floor plate specifies the number of ventral horn motor neurons will be examined by altering the number of floor plate cells and then monitoring motor neuron numbers. To test the second aim I will deprive the neural tube of its floor plate and then evaluate the type of neurons which develop in the dorsal horn. Whether the ventral horn motor neurons affect the development of the dorsal horn will be investigated by depriving the neural tube of ventral horn motor neurons and also be extirpating the floor plate and then grafting ventral horn motor neurons. The morphological and biochemical differentiation and innervation of muscles will be examined to determine sensory from motor neurons. The results of this investigation should provide a better understanding of the mechanisms responsible for cellular differentiation and pattern formation during normal development and also provide clues into the mechanisms of abnormal development of the nervous system.